You write, "I can believe that that could have been his line of thought but it says that he was prepared to take the risk of his rearguard not getting over bridge before the allies overwhelmed them, Which brings us back to Macdonald's mutterings about criminal indifference"
Considering that N. abandoned his army in Egypt and again in Russia, taking the chance of abandoning a few thousands of his rear guard in Leipzig would not have been a difficult one. After all, that was their duty.
Again, the only reason anyone expressed shock at the scene of Leipzig after the premature blowing of the bridge is because it was premature. If it had gone according to N.'s plan, they would have been singing of his glory and genius.
The interesting information would be tracking all the Genie (engineering) resources still present at Leipzig by Oct. 17. I believe that because the main engineering force was already at the Saale on N.'s orders to bridge that river and the engineering reinforcement group from the east was blocked from reaching Leipzig by Allied forces, that the engineering forces at Leipzig were extremely limited. N. may well have been forced to make the decision between the two engineering operations at hand: bridge mining or temp bridges. If he only had enough engineering forces for one job and not both, then that tells us that this is exactly the decision N. had to make. My view is in part based on the assumption that the engineering forces were so limited.